I do it so I can show it to iPhone users and they feel at home. They recognize the important icons and so they don't get hung up on that while they are exploring gestures etc.

The other reason is that the one thing Apple does better than anyone (and I am not a Mac person) is to create clean simple UI. I use solid black wall paper, and I like the way the dock looks with an OSX shelf under it... It's a nice clean look, No scrims, no clashing graphics, just the stuff I need. The first thing I did was delete all of the bright and busy wall paper that came with the phone. Same with my PC...

People really value being able to personalize... Remember the first android commercial? "If you want to be you, be you...." that was poking fun at the lack of customization on iPhone because they lock everything down. Palm needs to build some basic theme options into webOS like they did with PalmOS years ago, so it is available to all users without needing preware, IMHO.